1. Technical Field
This invention relates to inspection devices and, more particularly, to probes having a moveable stylus used to detect contact with an object such as a workpiece.
2. Background
Probes are often used by automated machine tool systems for purposes of detecting dimensional information about workpieces. Some of the known probes are referred to as touch probes in that they operate to transmit a signal to the machine controller when a probe stylus touches the workpiece. In general, touch probes include an industry standard shank portion located opposite the stylus so that the probe can be inserted into the machine in the same manner as the tools that actually remove metal from the workpiece. In use, the machine moves the probe relative to the workpiece until the stylus contacts the workpiece thereby removing the stylus from its rest position. The machine controller stores the X, Y and Z axes position of the probe stylus in its memory when the signal is received from the probe indicating that the stylus has contacted the workpiece. By touching the workpiece at several locations it is possible to calculate dimensions of the workpiece. This process is often referred to as "in-cycle gaging". Examples of some touch probe constructions are found in U.S. Pat. Nos. 4,535,543 to Linder; 4,553,332 to Golinelli et al and U.S. Pat. No. 4,562,646 to Dall'Aglio.
It is highly desirable for probes of this types to be rugged, permit a generous amount of stylus overtravel and still provide highly accurate repeatable measurements. The term "stylus overtravel" means the distance the stylus can be displaced from its rest position without harming the future repeatability of the probe. The need for good overtravel characteristics is due, for example, because the inertia of the machining tool often carries, the probe past the location where the stylus initially touches the workpiece under inspection. Thus, the stylus can be displaced by a relatively large degree and it is desirable for the probe to be capable of tolerating as much "overtravel" as possible without impairing characteristics of the probe components such as their elastic limits and the like which could degrade the accuracy of the probe. Of course, it would be very advantageous if these objectives can be met while at the same time permitting easy and economical manufacturing of the probe from both a labor and materials standpoint. It is believed, however, that some of the probe constructions of the prior art do not lend themselves to fulfilling these goals.